Synergistic combination of extreme pres-



United States Patent 3,125,527 SYNERGHSTIC CfiMBlNATlON 0F EXTREME PRES- SURE ADDITIVES F0212 LUBRICATING OILS Robert H. Krug, Cornwall, Raymond B. Tierney, Wappingers Falls, and Edwin C. Knowles, Poughkeepsie, N.Y., and Edward L. Kay, Akron, (Ohio, assignors to Texaco Inc, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 16, 1960, er. No. 49,841 8 Claims. (Cl. 252-463) This invention relates to an improved lubricating cornposition containing a combination of additives which exhibit synergistic extreme pressure pnoperties. More particularly, this invention relates to lubricating oils containing a combination of a bor'ate ester and a polymerized fatty acid for use in mineral oils and synthetic lubricants.

There is an ever increasing need for the improvement of the extreme pressure properties of lubricating oils used in heavy high speed machinery. This is particularly true for the lubrication of newly developed jet turbine and marine turbine engines. The present invention defines an additive combination possessing synergistic extreme pressure action which is particularly useful in the formulation of jet engine and marine engine turbine oils.

The synergistic extreme pressure additive combination of the invention comprises a borate ester and a polymerized fatty acid in a weight ratio of from 5 to 80 parts of borate ester per part of polymerized fatty acid.

The lubricating composition of the invention comprises [from 0.05-01 weight percent polymerized linoleic acid and 0.5 to 4.0 weight percent borate ester. The srnall percent concentration of fatty acid polymer which has only a slight etfect on the extreme pressure properties of the oils causes a significant and unexpected improvement of the extreme pressure properties of an oil containing borate ester which is a known extreme pressure agent.

The borate compounds employed in the present invention are organic boron compound which are stable, oilsoluble compounds containing the BOR group, wherein R is an organic radical. Suitable compounds of this class are those which do not decompose in the presence of oxygen at ordinary and moderately elevated temperatures and are substantially non-corrosive to metals, including copper and aluminum as for example under the conditions of the MIL-L-OUZIOSA copper strip corrosio n test, which is carried out for three hours at 250 F. The preferred compounds of this class are borate esters represented by the formula wherein R is a hydrocarbon radical. Hydrocarbon radicals represented by R may be al-kyl, aryl, alkaryl, or aralkyl radicals, or such radicals containing substituents of various types which do not substantially increase the chemical reactivity or corrosiveness of the compound.

Examples of suitable compounds of the above class include trimethyl borate, tri-n-propyl borate, tri-isobutyl bcrate, tristearyl borate, triphenyl bonate, tri-(nonylphenyl) borate, di-(Z-ethylhexyl) nonylphenyl borate, tri-(para-tertiaIy-butylphenyl) borate, tnicresyl borate, tribenzyl borate, tiri-(Z-phenylcyclohexyl) borate, tri- (di-isobutyl carbinyl) borate, tri-(tetrahydrofiurfuryl) 'borate, tri-(2,6,8-trimethyl-4-nonyl) borate, tri-cyclohexyl borate, tri-(7-ethyl-2amethyl-4-undecyl) borate, tetrabenzyl di bonate and tetra-(nonylphenyl) di-borate.

The concentration of the borate ester in the lubricant composition of the present invention fails between 0.5 to 4.0 weight percent of the total lubricant with the pre- 3,125,527 Patented Mar. 17, 1964 2 ferred concentration of between 1.0 and 2.0 weight percent usually being employed.

The polymerized fatty acid which is employed as the second component in the synergistic additive combination of the present invention can be represented as a dimer acid by the following general formula:

wherein R is a monovalcnt aliphatic hydrocarbon radical containing 4 to 10 carbon atoms, and R is a divalent aliphatic hydrocarbon radical containing 4 to 10 carbon atoms. The dimer acids are derived from reaction of two C to C ethylenic monocarboxylic aliphatic acids, at least one of which contains a conjugated diolefinic group. Although dimer acids may be formed by the reaction of a monoethylenic acid such as oleic with a con jugated polyethylenic acid such as linoleic acid dimer acids are usually formed by polymerization of two polyole-finic acids.

Polyethylenic conjugated acids useful in the preparation of the dimer acids of the invention are linoleic acid, linolenic acid and 13,15-docosadien0ic acid. Monoethylenic aliphatic monocarboxylic acids which can be reacted with polyethylenic acids to form dimer acids are 4-dodecenoic acid, myristoleic acid, palmitoleic acid, erucic acid and oleic acid. The conjugated polyethylenic aliphatic monocarboxylic acids and monoolefinic oarboxylic acids employed to form dime-r acids can be obtained by hydrolysis of vegetable oils such as soy bean oil, linseed oil, cottonseed oil, corn oil, castor oil, mustard seed oil, and peanut oil.

Linoleic acid dimers are the preferred second ingredient along with the borate esters as the extreme pressure agent of the present invention. The linoleic acid dimer has the following formula:

Examples of other polymerized fatty acids effective in the synergistic combination extreme pressure additive of the present invention are the trimer and higher polymerized fatty acids.

These polymer fatty acids are commercially available products and are prepared by known methods. One method entails steam heating unsaturated fatty acids in a pressure vessel at temperatures from 260-360" C. for about 3 to 10 hours to produce a polymerized product mainly consisting of a dimer acid. The dimer acid is then separated [from the resulting product by distillation.

Only small concentrations of the fatty acid dimer are necessary to exert their synergistic action in combination with the borate ester compound. The usual concentration of fatty acid dimer in the lubricating oil is in most cases from 0.05 to 0.1 weight percent inclusive.

The weight ratio of borate ester compound to polymerized fatty acid in the synergistic extreme pressure additive of the present invention expressed independently of the lubricating oil is from 5 to parts and preferably 10 to 40 parts of borate ester per part of polymerized fatty acid.

The base oils with which the novel extreme pressure additives of the present invention are used are the hydrocarbon lubricating oils, synthetic lubricating oils and mixtures thereof. The hydrocarbon oils include mineral, vegetable and animal oils, but particularly hydrocarbon mineral oils which can be paraffin base, naphthene base or mineral base oils of the residual or distillate type. The viscosity range of the mineral lubricating base oils is between 80 and 1000 SUS at F. The base oils usually have a flash point between 320 F. and 520 F, a pour point within the range of F. to F. and a viscosity index between 10 and 120. Particularly preferred oils are paraffin base oils which have been solvent dewaxed and clay percolated and which have SUS viscosity at 100 F. and between 300 and 600.

The synthetic lubricating base oils include high molecular weight polyalkylenes and high molecular weight high boiling liquid aliphatic dicarboxylic acid esters which possess excellent viscosity-temperature relationships and lubricating properties and are finding ever increasing utilization in lube oils and grease adapted for high and low temperature lubrication. Examples of this ester class of synthetic lubricant bases are the diesters of acids such as sebacic, adipic, azeiaic, alkenyl-succinic, etc.; specific examples of these diesters are di-Z-ethylhexyl sebacate, di-2- ethylhexyl azelate, di-2-ethylhexyl adipate, di-n-amyl sebacate, di-Z-ethylhexyLn-dodecyl succinate, di-Z-ethoxyethyl sebacate, di-2'-methoxy-2-ethoxyethyl sebacate (the methyl Carbitol diester), di-2-ethyl-2-n-butoxyethyl sebacate (the Z-ethylbutyl Cellosolve diester), di-Z-butoxyethyl azelate (the n-butyl Cellosolve diester) and di-2'-nbutoxy-Z-ethoxy-ethyl-n-octyl succinate (the n-butyl Carbitol diester).

A preferred high molecular weight polyallzylene is polybutcne having a molecular weight range of from 500 1500.

Polyester lubricants formed by a reaction of an aliphatic dicarboxylic acid of the type described above, a glycol and a monofunctional aliphatic monohydroxy alcohol or an aliphatic monocarboxylic acid in specified mole ratios are also employed as the synthetic lubricating base in the compositions of this invention; polyesters of this type are described in U.S. 2,628,974. Polyesters formed by reaction of a mixture containing specified amounts of dipropylene glycol, ebacic acid and 2-ethylhexanoic acid and of a mixture containing adipic acid, diethylene glycol and Z-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Polyalkylcne ethers as illustrated by polyglycols are also used as the lubricating base in the compositions of this invention. Polyethylene glycol, polypropylene glycol, polybutylene glycols and mixed polyethylene-polypropylene glycols are examples of this class of synthetic lubricating bases.

The sulfur analogs of the above-described diesters, polyesters and polyaikylene ethers are also used in the formulation of the lubricating compositions of this invention. Dithioesters are exemplified by di-Z-ethylhexyl thiosebacate and di-n-octyl thioadipate; polyethylene thioglycol is an example of the sulfur analogs of the polyalkylene glycols; sulfur analogs of polyesters are exemplified by the reaction product of adipic acid, thioglycol and Z-ethyl mercaptan.

The lubricating compositions which are employed in accordance with the present invention comprise essen tially a lubricating oil containing about 0.5 to 4.0 weight percent of a borate ester of the character described above and about 0.05 to 0.1 weight percent of a fatty acid polymer of the character described above. In addition the compound may contain various other additives such as are conventionally employed in lubricating oils such as detergents anti-oxidants, viscosity improvers, anti-foam agents, corrosion inhibitors, etc.

Alkyl-substituted phenols are usually incorporated in the lubricants of the invention as anti-oxidants. The preferred and most commonly used alkylphenol anti-oxidant is 2,6-di-tertiary butyl-4-methylphenol which is commercially available from a number of sources. Examples of other phenolic type anti-oxidants which may be employed are 2,6-di-tertiary butylphenol; 2,6-di-tertiary amyl-4 methylphenol; and 2,6 di isopropyl 4 methyl phenol. Hindered phenols of this type are employed in concentra tions between 0.1 and 1.0 weight percent. Phenothiazine is very widely used as an an.i-oxidant in ester base lubricanis.

Although hindered phenol type anti-oxidants are the most widely used anti-oxidants in the lubricant compositions of the invention, aryl-substituted amine anti-oxidants such as phenyinaphthylamine, phenylene diamine, and diphenyiamine are also used in lubricants in conjunction with the synergistic extreme pressure additive combination of the invention. The amine anti-oxidants are employed in the same concentrations as the hindered phenol anti-oxidant.

Anti-rust compounds used in connection with the synergistic extreme pressure additive of this invention are the alkyl-substituted aliphatic dicarboxylic acids such as alkenyl-succinic acids, alkyl-maleic acids and alkyl-succinic acids. These aliphatic-substituted dicarboxylic acids are usually used in conjunction with a minor portion of an acid ester of an alkyl phosphate. A mixture of monoand dialauryl esters of phosphoric acid is widely used in conjunction with an aliphatic-substituted dicarboxylic acid as as anti-rust additive mixture. A detailed description of this additive mixture is found in U.S. Patent 2,452,321, which issued Oct. 26, 1948, to John A. Patterson and Herman D. Kluge, and which is assigned to The Texas Company. The dicarboxylic acid is usually employed in a concentration between 0.01 and 0.1 weight percent and the alkyl phosphate in a concentration between 0.0001 and 0.03 weight percent.

Organic silicones are normally incorporated in the lubricants of the invention to impart anti-foam properties thereto. The silicones are usually of the dialkyl or mixed alkyl-aryl silicone type. Dimethyl silicone is normally employed as the anti-foam agent. The silicone is incorporated in the lubricant by means of a kerosene concentrate containing 5 to 15 Weight percent silicone. A very satisfactory anti-foam agent is a kerosene concentratecontaining 10 weight percent dimethyl silicone. The kerosene concentrate is employed in an amount suflicient to provide a silicone polymer concentration of from 50 to 250 parts per million based on the total lubricant composition.

The synergistic extreme pressure effectiveness of the organic boron compounds of the present invention under conditions of turbine lubrication is shown by the results of gear tests simulating these conditions in the following table. The testing of the El. properties in the combination of the additives of the present invention was performed using the test procedure of a high speed gear scuff test known as the Ryder gear test. This test is intended for the evaluation of the scuff-limited load-carrying ability of those lubricants used in reduction and accessory drives of turbo-jet and turbo-prop engines. The method of test provides for the running of two spur gears in a Pratt and Whitney gear and lubricant tester (also termed the Ryder gear tester). The face width of the driven gear was 0.937 inch and the face width of the driving gear was 0.25 inch. The dynamometer speed of the gear tester was put up to 4600 r.p.m. and a loading pressure of 2.5 p.s.i. applied. After running for 15 minutes the tester was shut down and the driving gear removed and an estimate of the percentage of tooth area scuffed on each tooth of that gear was made. The gear was replaced and the above procedure continuously repeated using a higher loading pressure at each repetition until 22.5 percent of the total tooth face area on the driving gear had been scuffed, the load corresponding to this point being considered the scuff load. The loading pressures to be successively used were as follows; 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 25, 30, 35, 40, 45, 50, 60, 70 and p.s.i. A tooth load conversion factor of 18.5 pounds, which was a constant calculated from measured data from the tester, was multiplied by the loading pressure at the scuff load and the result divided by the width of the driving gcar (0.25) to obtain the tooth load in pounds per inch.

In Table I there are presented data providing the synergistic extreme pressure action of a mixture of borate ester and fatty acid dimer additives. In Table I the oil used is designated as base oil A and is a synthetic oil 4. A synthetic ester base lubricating oil containing 0.5

to 4.0 weight percent of a borate ester having the general comprising pentaerythritol tetracaproate. formula:

Table 1 Weight Percent Compositions Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12

Base Oil A 98. O 99. 0 98. 9 96. 9 97. 0 95 97 94. 95 94. 9 98. 5 98. 45 98. 4 Phenothiazine 1. 0 1. 0 1. 0 1.0 1. 0 1 1. 0 1. 0 1. 0 1. 0 1. 0 Tribenzyl borate 1.0 2.0 2.0 2 0 4. 0 4. 0 Tri-(di-isobntyl carbinyl) borate.-. 0 5 0. 5 0 5 Linoleic acid dimer 0.1 0. 1 O 05 0.05 0.1 0. 05 0 1 Ryder Gear Test 2, 365 2, 390 2, 768 3, 420 2, 445 3, 070 3, 370 3, 608 2, 510 3,080 3 247 The data in the foregoing table prove that mixtures of borate esters and fatty 'acid dimers in the ratio disclosed possess a surprising synergistic extreme pressure action. The additon of 0.5-1.0 percent of linoleic acid dimer in the base oil A improves the ability of the lubricant to withstand a load to about 300400 lbs. per inch over the base oil alone. However, when this same amount is used in combination with 0.5-4.0 percent of the borate ester the increase in the load carrying capacity is about 400800 lbs. per inch over the base oil containing just 0.5-4.0 percent borate ester. This is very significant in view of the fact an additional 0.5-4.'-0 percent of the borate ester only raised the load carrying ability of the lubricant 0-200 lbs.

We claim:

1. A synergistic extreme pressure additive combination for lubricants consisting essentially of from 5 to 80 parts by Weight of a borate ester having the general formula:

wherein R is a hydrocarbyl radical having from 1 to 18 carbon atoms and from 0.05 to 0.1 weight percent of a fatty acid selected from the group consisting of linoleic acid dimer, linolenic acid dimer and 13,15-docosadienoic acid dimer.

5. A synthetic ester base lubricating oil containing from 0.5 to 4.0 weight percent tribenzyl borate and from 0.05 to 0.1 weight percent of linolenic acid dimer.

6. A synthetic ester base lubricating oil containing from 0.5 to 4.0 weight percent of tri(diisobutylcarbinyl) borate and from 0.05 to 0.1 weight percent of linoleic acid dimer.

7. A lubricating oil according to claim 4 in which said ester base lubricating oil is pentaerythritol tetracaproate.

S. A pentaerythritol tetracaproate lubricating oil containing 0.5 to 4.0 weight percent of tribenzyl borate, 0.05 to 0.1 weight percent of linoleic acid dimer and an effective anti-oxidant amount of phenothiazine.

References Cited in the file of this patent UNITED STATES PATENTS 2,053,474 Graves et a1. Sept. 8, 1936 2,154,098 Loane et al Apr. 11, 1939 2,160,917 Shoemaker et a1 June 6, 1939 2,883,339 Richardson Apr. 21, 1959 2,950,250 Fainman Aug. 23, 1960 3,048,542 Tierney et a1 Aug. 7, 1962 3,074,886 Tierney et al Jan. 22, 1963 FOREIGN PATENTS 814,864 Great Britain June 10, 1959 578,779 Canada June 30, 1959 

1. A SYNERGISTIC EXTREME PRESSURE ADDITIVE COMBINATION FOR LUBRICANTS CONSISTING ESSENTIALLY OF FROM 5 TO 80 PARTS BY WEIGHT OF A BORATE ESTER HAVING THE GENERAL FORMULA: 